Carotenoids carotenoid absorption

The measurement of carotenoid absorption is fraught with difficulties and riddled with assumptions, and it is therefore a complex matter. Methods may rely on plasma concentration changes provoked by acute or chronic doses, oral-faecal mass balance method variants and compartmental modelling. 

As mentioned earlier, physiological concentrations of carotenoids in vivo are in the micromolar range, mainly because of limited bioavailabiUty. Also, the antioxidant efficiencies of carotenoids after absorption are probably limited. Concentrations before absorption are much higher and can justify possible antioxidant actions in vivo. To test this hypothesis, Vulcain et al. developed an in vitro system of lipid peroxidation in which the oxidative stress is of dietary origin (metmyoglobin from meat) and different types of antioxidants (carotenoids, phenols) are tested. 

A group of competing reactions takes place when carotenoids are exposed to light. When the incidence of light energy overlaps the carotenoid absorption region. 

Reboul et al., 2007a,b). As mentioned earlier the competitive uptake occurs also in the presence of a mixture of carotenoids where absorption of lutein is inhibited by [1-carotene but not by lycopene (Reboul et al., 2005). This indicates that the presence of a mixture of different lipophilic substrates can strongly influence the uptake of certain carotenoids. It has also been demonstrated that cultured Caco-2 cells secrete (3-carotene, preferentially within micelles rich in long fatty acids (Yonekura et al., 2006), suggesting that carotenoids can be stored in the cell or secreted depending on the absence or presence of appropriate carotenoid acceptors. 

Independent Pathways of Retinol and Carotenoid Absorption in Caco-2 Cells ... 

Carotenoid absorption and metabolism have been comprehensively reviewed (Erdman et al., 1993 Parker, 1996 van Vliet, 1996 Furr and Clark, 1997 Yeum and Russell, 2002) and this chapter will focus only on recent advances in these areas. A particular emphasis will be placed on studies that used in vitro and cell culture models as tools to understand better the mechanisms of absorption on the molecular level. 

Thus, in contrast to previous in vivo models, this in vitro model provides the possibility of dissociating experimentally two important processes of the intestinal carotenoid absorption cellular uptake and secretion. Under conditions mimicking the postprandial state (TC OA supplementation), differentiated Caco-2 cells were able (1) to take up carotenoids at the apical side and to incorporate them into CM and (2) to secrete them at the basolateral side, associated with CM fractions. In this model, no attempt has yet been made to reproduce the in vivo physiochemical conditions occurring in the intestinal lumen, such as carotenoid release from the food matrix and solubilization into mixed lipid micelles. Carotenoids were delivered to Caco-2 cells in aqueous suspension with Tween 40 (During et al., 2002). Using this cell culture system in conjunction with an in vitro... 

THE HUMAN CACO-2 INTESTINAL CELL MODEL A VALUABLE TOOL FOR STUDYING CAROTENOID ABSORPTION... 

Competition resulting in a decrease of global carotenoid absorption can occur at many steps of the digestion process, including the transfer of carotenoids into mixed micelles, transport across... 

In conclusion, the Caco-2 cell monolayer model has given original data on the competition effect of several nutrients on carotenoid uptake. Most of these data have been confirmed in several in vivo studies, including clinical studies, confirming that this model is a valuable tool to study competition effects on carotenoid absorption. 

Carotenoids are highly lipophilic an active area of research concerns how carotenoids interact with and affect membrane systems (see Chapters 2 and 10). Also, the lipid solubility of these compounds has important implications for carotenoid intestinal absorption (see Chapter 17) models such as the Caco-2 cell model are being used to conduct detailed studies of carotenoid absorption/ competition for absorption (Chapter 18). The lipid solubility of these carotenoids also leads to the aggregation of carotenoids (see Chapter 3). Carotenoids aggregate both in natural and artificial systems, with implications for carotenoid excited states (see Chapter 8). This has implications for a new indication for carotenoids, namely, serving as potential materials for harnessing solar energy. 

Nevertheless, the avena coleoptile exhibits a curvature to unilateral UV-illumina-tion with a satisfactory log-linear response/time relationship38) (the bending mode is similar to that observed for the second positive curvature which develops from the coleoptile base cf. 2.2). Fig. 5 338) shows that the double-peaked action spectrum does not match neither flavin (Fig. 5 5,16S)) nor carotenoid absorption (Fig. 5 4,183)), most likely excluding both as photoreceptors. The growth hormone auxin (cf. 2.4 and Scheme 1) has been discussed to be a possible photoreceptor. However, in this case, this is not supported by the action spectrum either. 

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